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„We are not talking about cosmology...“ (A. Sozzetti). The visitor from an ancient galaxy A planetary companion around an old, metal-poor Red Horizontal Branch star. R. J. Klement, J. Setiawan, Th. Henning, H.-W. Rix, B. Rochau, T. Schulze-Hartung, J. Rodman (ESA/ESTEC,NL). - PowerPoint PPT Presentation
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„We are not talking about cosmology...“
(A. Sozzetti)
The visitor from an ancient galaxy
A planetary companion around an old, metal-poor Red Horizontal Branch star
R. J. Klement, J. Setiawan, Th. Henning, H.-W. Rix, B. Rochau,
T. Schulze-Hartung, J. Rodman (ESA/ESTEC,NL)
Do planets exist in external galaxies? Probably, but can we find out?
Motivational background
Do planets exist in external galaxies? Probably, but can we find out?
Motivational background
Yes we can!
Do planets exist in external galaxies? Probably, but can we find out?
Observe nearby halo stream stars!
Motivational background
Yes we can!
Target selectionThe Helmi stream (Helmi et al. 1999)
Target selectionThe Helmi stream (Helmi et al. 1999)
SErGiO
SErGiOStar of Extra-Galactic Origin
Stellar parameters Literature & our results
Spectral typeBrightness (V)DistanceEffective temperatureRadiusSurface gravity (log g)Stellar massMetallicity [Fe/H]Projected rotational velocityConfirmed membershipEvolutionary stage
F29.84 mag700 pc6025 K6.7 RϿ
2.690.82 MϿ
-2.0910.3 km/sHelmi streamRHB
Radial Velocity
FEROSSept. 2009 – July 2010
36 RV measurements
550 spectral lines for RV computations
semi-amplitude 120 m/s
uncertainty ~ 50 m/s
FAP = 5.5 x 10e-6
Sources of RV variation
Starspots
Line-profile asymmetry (bisector, BVS)
Ca II variations (K & H, IR triplet)
Other spectroscopic activity indicator
(Hα, Teff variation, …)
Photometric variations
If the stellar activity can be excluded
Rotational modulation
Stellar pulsations
Rotational modulation
Stellar pulsations
Companion
Sources of RV variation
periodic variations of - the BVS ~ 5 days- CaII λ8498 ~ 6 days→ rotational modulation→ Vrot ~60 km/s SuperWASP photometry
(~3600 data points)→ stellar pulsations
Planet: SerGiO jr.Setiawan, Klement et al., submitted
Parameter Value
PeriodAmplitudeEccentricitySemimajor axisMinimum mass (m sin i)
16.2 days120 m/s0.280.116 AU1.3 M(Jup)
The estimated minimum mass places the companion in the substellar regime.
What is interesting?
Sergio has an extra-galactic origin Sergio has the lowest metallicity among known
planet host stars, [Fe/H] = -2.09 ± 0.25 dex
What is interesting?
The planet has survived the
RGB phase during the stellar evolution.
Probably, at the beginning the planet had a larger orbit, but then spiraled in to a closer orbit
The star is a fast rotator.
Sign that the inner planets have been engulfed already(?)
Conclusions
Planets can indeed form around metal-poor stars as low as [Fe/H] ~ - 2
Under certain circumtances planets can survive the red giant phase. The orbits may be changed during the stellar evolution.
SErGiO jr is the first planet detected in a tidal stellar stream and probably the first known exoplanetary system with an extragalactic origin.